Modern aircraft generally possess a synthetic vision system called “SVS”. This system allows a synthetic image of the exterior landscape, generally comprising piloting or navigation information, to be presented to the crew.
An SVS system comprises a cartographic database representative of the terrain overflown, a geolocation system, an inertial platform, sensors measuring altitude and speed, electronic calculation means and one or more viewing devices installed in the cockpit of the aircraft. The geolocation system is of the “GPS” type, the acronym standing for “Global Positioning System”. Generally, the synthetic image is displayed on the viewing screens which are situated on the front face of the aircraft's instrument panel.
The synthetic image is a three-dimensional view of the exterior represented in the most realistic possible manner. The viewpoint displayed is generally on the axis of the craft. This image comprises a symbology intended to aid piloting and navigation. By way of example, FIG. 1 represents in a stylized manner and with the constraints inherent in patent figures, an image of this type. It comprises a view of the exterior landscape as background and a symbology represented in black lines. The latter comprises essentially:                The so-called “ADI” parameters, the acronym standing for “Attitude Director Indicator” which give the attitude of the craft, that is to say its angular position in terms of roll and pitch. Conventionally, the position of the craft is represented by a symbol 1 called an aircraft mockup centred on a scale 2 graduated in degrees. In FIG. 1, the scale 2 is represented by two series, spaced apart by 5 degrees, of symmetric symbols 3. It also comprises a horizon bar 4;        The air speed scale 5. This is a vertical scale situated on the left of the attitude scale. It represents the speed of the craft and is generally graduated in knots. In FIG. 1, the air speed is about 155 knots;        The altitude scale 6. This is a vertical scale situated on the right of the attitude scale. It is generally graduated in feet. In FIG. 1, the altitude of the craft is 1000 feet. This scale 6 is symmetric with the speed scale 5 with respect to the ADI scale 2;        The speed vector 7. This is generally represented by a circle comprising two symmetric horizontal segments and a vertical segment. It represents the angular direction that the speed of the craft makes with the angular position of the craft.        
When the flight conditions are nominal, the speed vector is close to the aircraft mockup and the representation of the symbology does not pose any particular problems. However, when there is a strong crosswind, the speed vector is shifted and if it is represented in a conformal manner, it will cross the speed or altitude scales before exiting the field of the image. To avoid this first problem, onwards of a certain shift, the speed vector is no longer represented in a conformal manner but dashed so as to signify to the pilot that his position is no longer conformal. This change of appearance of the speed vector is illustrated in FIG. 2.
A second problem arises. If the aircraft is in the landing phase, the speed vector is representative of the direction followed by the craft in order to reach the landing runway. Consequently, the representation of the image of the runway itself is shifted, is no longer centred and becomes overlaid on the speed or altitude scales. Thus, the image of the runway loses in terms of visibility. In FIG. 2, the runway 10 is represented by two white lines.